1. Field of the Invention
The present invention relates to a cylindrical electric double-layer capacitor, and particularly to a cylindrical electric double-layer capacitor having a cylindrical sealed vessel that seals an electrode roll and an electrolyte solution. The electrode roll being made by swirlingly rolling a superposed assembly comprising a band-shaped positive pole, a band-shaped negative pole and two band-shaped separators sandwiching one of the band-shaped positive and negative poles. Each of the band-shaped positive and negative poles has a band-shaped collector and a pair of polarizing electrodes formed in a laminated manner on opposite surfaces of the band-shaped collector.
2. Description of the Related Art
If a gap exists between an inner peripheral surface of the sealed vessel and an outer peripheral surface of the electrode roll, when a vibration or a shock acts on the electric double-layer capacitor, the electrode roll is vibrated, whereby the polarizing electrodes may be peeled off from the collector. Such a situation causes an increase in internal resistance, a reduction in a self-discharging characteristic and other like effects.
In a conventional measure, a plurality of annular projections are formed by drawing on an inner peripheral surface of a metal vessel, so that they are arranged at predetermined intervals in the axial direction, and tops of the annular projections abut against an outer peripheral surface of an electrode roll (see Japanese Patent Application Laid-open No. 2000-243670).
With the above construction, however, when rubbing due to vibration or the like occurs between the outer peripheral surface of the electrode roll and each of the annular projections, the following disadvantages often occur: if the outer peripheral surface of the electrode roll is defined by a separator, the separator may be broken, and if the outer peripheral surface of the electrode roll is defined by the polarizing electrode, the electrode may be peeled off from the collector.
Accordingly, it is an object of the present invention to provide a cylindrical electric double-layer capacitor which can eliminate the above-mentioned disadvantages by applying a contrivance to the electrode roll.
To achieve the above object, according to the present invention, there is provided a cylindrical electric double-layer capacitor comprising a cylindrical sealed vessel housing an electrode roll and an electrolyte solution. The electrode roll is formed of a superposed assembly comprising a band-shaped positive pole, a band-shaped negative pole and two band-shaped separators sandwiching one of the band-shaped positive and negative poles. Each of the band-shaped positive and negative poles has a band-shaped collector and a pair of polarizing electrodes formed in a laminated manner on opposite surfaces of the band-shaped collector. An outer diameter D1 of the electrode roll before being accommodated in the sealed vessel and an inner diameter D2 of the sealed vessel are in a relationship of D1 less than D2. In a state in which the electrode roll has been accommodated in the sealed vessel along with the electrolyte solution, the outer diameter D1 of the electrode roll and the inner diameter D2 of the sealed vessel are brought into a relationship of D1=D2 by at least one of swelling of the polarizing electrodes caused by the electrolyte solution and expansion of the polarizing electrodes caused by electrical charge.
In the capacitor, when the electrode roll is accommodated in the sealed vessel along with the electrolyte solution, the electrode roll can be naturally adhered to the sealed vessel after the accommodation or during electrical charge. Thus, even in a situation where the polarizing electrode would possibly be peeled off from the band-shaped collector due to a difference in elongation between the band-shaped collector and the polarizing electrode, the polarizing electrode can be always adhered to the band-shaped collector to avoid an increase in internal resistance, a reduction in a self-discharging characteristic and other like electrical effects. In addition, it is unnecessary to subject the vessel to a drawing process, so that an equipment for drawing is not required. According to a second feature of the present invention, the polarizing electrode includes a conductive filler having a high hydrophilicity.
According to a third feature of the present invention, the polarizing electrode includes activated carbon which is made by subjecting a source material for easily-graphitable carbon to a carbonizing treatment and an activating treatment and which is expanded during electrical charge.
With the second and third features, the cylindrical electric double-layer capacitor can be formed easily and reliably.
According to a fourth feature of the present invention, the band-shaped collector is formed of a metal foil, and an elongation xcex4 of the metal foil in the electrode roll is equal to or higher than 4% when the metal foil is broken.
With the fourth feature, in the cylindrical electric double-layer capacitor, it is possible to reliably avoid a damage due to the elongation of the band-shaped collector formed of the metal foil.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.